1. Field of the Invention
This invention relates to a means for cutting a paper web into a number of pages, and, more particularly, to a means for cutting a paper web pulled from a supply roll in a point-of-sale terminal into a number of sales receipts.
2. Description of the Related Art
Many machines handling paper, such as printers, include mechanisms for cutting a paper web into a number of sheets, with each paper cutting mechanism generally being a shear device, in which one blade passes across another blade to cut the paper.
A widely-used paper cutting mechanism is a shear paper cutter, in which one blade passes over the other in a straight path. However, when the moving blade returns after cutting the paper, it tends to bend the edge of the paper back, sometimes causing a jam during subsequent movement of the paper. Furthermore, the blades contact one another during movement in both the cutting direction and the reverse direction, causing unnecessary blade wear and power consumption.
A number of shearing devices are described in the patent literature. For example, U.S. Pat. No. 3,250,165 describes a paper cutter using a severing device including a resilient mounting to ensure that a traveling point contact occurs between the blades during shearing. This is achieved by locating a portion of a movable blade in back of a fixed blade, with the moving blade being angled with respect to the fixed blade to form a xe2x80x9cVxe2x80x9d, so that the apex of the xe2x80x9cVxe2x80x9d travels along the fixed blade during the cutting stroke. Also, the severing device directs the leading end of the material, from which a length has been severed, back into a given path.
U.S. Pat. No. 5,749,277 describes a cutting mechanism for a receipt printing machine, which has paper dispensed from a paper-supply roll. The cutting mechanism has a xe2x80x9cVxe2x80x9d-shaped guillotine blade that is held in a blade holder. The blade is driven through the blade holder against a stationary blade and into cutting contact with a paper web containing receipt indicia.
U.S. Pat. No. 5,237,901 describes a shear assembly for cutting hard brittle materials, such as amorphous metals used in transformers. A compensating link arrangement is operatively associated with one of two blades in the shear assembly. The angular position of the links may be selectively adjusted to alter a horizontal force component that counteracts a separation force associated with the blades during a cutting stroke.
What is needed in the devices of each of these patents is a mechanism for separating the blades following the cutting stroke, in order to reduce wear, noise, and power consumption.
The IBM Technical Disclosure Bulletin, Vol. 40, No. 4, April, 1997, describes a combination paper feed and cutter drive for a printer, eliminating a need for a separate motor to drive the paper cutter. A single stepper motor, a gear train, and two one-way clutches are used to drive paper through a thermal print mechanism and to drive a scissors-type cutter embodiment. One direction of the motor is used to feed the receipt paper, and the other direction is used to cut the receipt. The motor drives an idler gear, which in turn drives a thermal platen roller through a thermal clutch assembly which is a one-way clutch causing the thermal platen roller to rotate only in one direction. The motor also drives a cutter clutch drive gear, which in turn drives a shaft within a cutter clutch assembly which is coupled through a one-way clutch to a gear that drives the cutter drive gear. The cutter drive gear only rotates in its respective direction, except for small rotations in the reverse direction to ensure that the cutter is in an open position while paper is being fed. Reverse drag of the cutter clutch assembly provides a torque to reverse the cutter drive gear.
A general problem associated with using a single motor or drive to provide two or more functions, as described in the preceding paragraph, is that the mechanism can become jammed or otherwise inoperable because information regarding its state of operation can be lost in the event of an electrical power failure or in the event that parts of the mechanism are manually moved during an attempt to repair the mechanism or to clear a jam condition. What is needed is a mechanism which can be returned to a normal starting point even if such events occur.
It is a first objective of the present invention to provide a means for holding cutting blades within a paper cutter together during a cutting stroke, and for holding these blades apart during a return stroke following the cutting stroke.
It is a second objective of the present invention to provide a means for returning a paper cutting mechanism, operating in an alternating fashion with a paper feeding mechanism, to an operational starting point following a power failure or following the manual movement of parts within the mechanism.
It is a third objective of the present invention to minimize the width of a point-of-sale printer.
In accordance with a first aspect of the present invention, there is provided a paper cutter for a printer, in which the paper cutter includes a stationary knife blade, a moving knife blade, a blade holder, and first and second drive mechanisms. The blade holder holds the moving knife blade and moves with the moving knife blade. The first drive mechanism moves an edge of the moving knife blade in a first direction across an edge of the stationary knife blade to cut a paper web extending between the moving knife blade and the stationary knife blade, and additionally moves the edge of the moving knife blade opposite the first direction. The second drive mechanism moves the edge of the moving knife blade in a second direction away from the stationary knife blade and opposite the second direction into contact with the stationary knife blade.
The moving knife blade is moved in the first direction in contact with the stationary knife blade. The moving knife blade is moved opposite the first direction as the moving knife blade is held away from the stationary knife blade.